The centre of mass of an extended body on the surface of the earth and its centre of gravity:

Four masses are arranged along a circle of radius $1 \ m$ as shown in the figure. The center of mass of this system of masses is at

The centre of mass is a point:

Look at the drawing given in the figure which has been drawn with ink of uniform line-thickness. The mass of ink used to draw each of the two inner circles,and each of the two line segments is $m$. The mass of the ink used to draw the outer circle is $6m$. The coordinates of the centres of the different parts are: outer circle $(0,0)$,left inner circle $(-a, a)$,right inner circle $(a, a)$,vertical line $(0,0)$ and horizontal line $(0,-a)$. The $y$-coordinate of the centre of mass of the ink in this drawing is

Distinguish between the center of mass and the center of gravity.

$A$ large number of particles are placed around the origin, each at a distance $R$ from the origin. The distance of the center of mass of the system from the origin is